8.4 Neurologic Examination: Motor and Sensory Testing
Key Takeaways
- Manual muscle testing uses the 0–5 Medical Research Council scale: 0 = no contraction, 1 = flicker, 2 = movement with gravity eliminated, 3 = movement against gravity, 4 = movement against some resistance, 5 = normal strength.
- Upper extremity myotomes: C5 deltoid/biceps, C6 wrist extension/biceps, C7 elbow extension/triceps and wrist flexion, C8 finger flexion, T1 intrinsic hand muscles (abductor digiti minimi).
- Lower extremity myotomes: L2 hip flexion, L3 knee extension (quadriceps), L4 ankle dorsiflexion (tibialis anterior), L5 great toe extension (EHL), S1 ankle plantarflexion (gastrocnemius/soleus).
- Upper motor neuron lesions produce spasticity, hyperreflexia, Babinski sign, and no fasciculations; lower motor neuron lesions produce flaccidity, hyporeflexia, fasciculations, and atrophy in a segmental or peripheral nerve distribution.
- Deep tendon reflex grading: 0 absent, 1+ diminished, 2+ normal, 3+ brisk without spread, 4+ hyperactive with clonus; asymmetric reflex loss with weakness localizes to a specific root or peripheral nerve.
8.4 Neurologic Examination: Motor and Sensory Testing
Motor and sensory examination is the backbone of neurologic localization on NBCE Part II. Vignettes present a pattern of weakness, numbness, and reflex changes and ask you to identify the nerve root, peripheral nerve, or central pathway involved. The boards test three overlapping frameworks: myotomes (motor nerve root level), dermatomes (sensory nerve root level), and UMN versus LMN pattern recognition. Mastering these lets you distinguish C6 radiculopathy from carpal tunnel syndrome, L5 radiculopathy from peroneal neuropathy, and cervical myelopathy from isolated radiculopathy — all high-frequency Part II scenarios.
Manual Muscle Testing (0–5 Scale)
| Grade | Definition |
|---|---|
| 0 | No visible or palpable contraction |
| 1 | Flicker or trace contraction, no joint movement |
| 2 | Active movement with gravity eliminated |
| 3 | Active movement against gravity only |
| 4 | Active movement against some resistance |
| 5 | Normal strength against full resistance |
Grade 3 is the breakpoint: if a patient cannot move against gravity, the lesion is substantial. Part II may describe "4/5 weakness of wrist extension" and ask which root is affected (C6).
Cervical Myotomes and Dermatomes
| Root | Key muscle test | Dermatome territory |
|---|---|---|
| C5 | Shoulder abduction (deltoid) | Lateral arm |
| C6 | Elbow flexion (biceps); wrist extension | Lateral forearm, thumb, index finger |
| C7 | Elbow extension (triceps); wrist flexion | Middle finger, posterior arm |
| C8 | Finger flexion (FDP) | Ring and little fingers, medial forearm |
| T1 | Hand intrinsics (abductor digiti minimi) | Medial arm (axilla) |
Part II trap: C6 radiculopathy weakens biceps and wrist extensors with numbness in the thumb/index; carpal tunnel (median nerve, C6–C7 fibers) also affects the thumb and index but spares the deltoid and biceps — always test proximal muscles to separate root from peripheral entrapment.
Lumbosacral Myotomes and Dermatomes
| Root | Key muscle test | Dermatome territory |
|---|---|---|
| L2 | Hip flexion (iliopsoas) | Anterior upper thigh |
| L3 | Knee extension (quadriceps) | Anterior thigh, medial knee |
| L4 | Ankle dorsiflexion (tibialis anterior) | Medial leg, medial malleolus |
| L5 | Great toe extension (EHL) | Dorsum of foot, great toe web |
| S1 | Ankle plantarflexion (gastroc-soleus) | Lateral foot, heel |
Part II trap: Foot drop (weak dorsiflexion) localizes to L4–L5 (common peroneal/fibular nerve) but can arise from L5 radiculopathy, peroneal nerve compression at the fibular head, or sciatic nerve injury — check hip abduction (L5 gluteus medius) and SLR to separate root from peripheral nerve.
Sensory Testing Modalities
Test each modality deliberately; loss of one modality with preservation of others localizes the pathway:
- Light touch: Spinothalamic and dorsal column (rough screen)
- Pinprick and temperature: Lateral spinothalamic tract (anterior cord)
- Vibration and proprioception: Dorsal columns (posterior cord)
Peripheral neuropathy (diabetes, B12 deficiency) typically causes stocking-glove loss of pinprick and vibration distally. Radiculopathy causes a dermatomal strip. Cord lesions produce a sensory level on the trunk below the lesion.
Sensory level and cord syndromes
- Anterior cord syndrome: Motor paralysis and pain/temperature loss below the lesion; proprioception preserved (dorsal columns spared).
- Brown-Séquard (hemisection): Ipsilateral proprioception and motor loss; contralateral pain/temperature loss 1–2 levels below.
- Central cord syndrome: Upper extremity weakness and sensory loss greater than lower extremities (hyperextension injury in cervical spondylosis).
Deep Tendon Reflexes
| Reflex | Nerve root | Tendon |
|---|---|---|
| Biceps | C5–C6 | Biceps |
| Brachioradialis | C6 | Distal radius |
| Triceps | C7 | Triceps |
| Patellar (knee jerk) | L3–L4 | Quadriceps |
| Achilles (ankle jerk) | S1 | Gastrocnemius/soleus |
Grading: 0 absent, 1+ diminished, 2+ normal, 3+ brisk, 4+ hyperactive with clonus/spread.
Reflex asymmetry is more meaningful than bilateral brisk reflexes. Absent ankle reflex with S1 weakness supports S1 radiculopathy. Hyperreflexia with Babinski supports UMN disease (myelopathy, stroke).
UMN vs LMN Pattern Recognition (Motor Exam)
| Feature | UMN | LMN |
|---|---|---|
| Weakness pattern | Pyramidal (extensors > flexors in LE) | Segmental or nerve distribution |
| Tone | Spasticity | Flaccidity |
| Reflexes | Hyperreflexia, clonus | Hyporeflexia, areflexia |
| Babinski | Positive | Negative |
| Fasciculations | No | Yes |
| Atrophy | Minimal | Prominent |
Cervical myelopathy (UMN): gait disturbance, hyperreflexia in the legs, Hoffmann sign, Babinski, possible Lhermitte sign — may coexist with radiculopathy at one level. ALS shows mixed UMN and LMN signs without sensory loss.
Integrating Motor, Sensory, and Reflex Findings
A complete root-level picture requires all three:
Example — L5 radiculopathy: Weak EHL (motor L5), numbness dorsum of foot/great toe (sensory L5), diminished or normal reflexes (no dominant L5 reflex — may have slight medial hamstring), positive SLR.
Example — C7 radiculopathy: Weak triceps and wrist flexors, numbness in the middle finger, diminished triceps reflex.
Example — Carpal tunnel (median nerve): Weak APB (thenar), numbness thumb-index-middle/radial ring, normal proximal strength and reflexes, positive Phalen/Tinel.
Part II Traps
Do not localize weakness to the wrong root by testing the wrong muscle — ankle dorsiflexion is L4–L5 (primarily L4 tibialis anterior), but great toe extension is L5 (EHL). Do not assume bilateral brisk reflexes alone mean pathology — anxiety and age increase tone. Sensory examination must match the motor level; isolated numbness without weakness may still be radiculopathy but warrants careful dermatomal mapping. Finally, saddle anesthesia with urinary retention is cauda equina until proven otherwise — no amount of orthopedic testing changes the emergency referral.
A 40-year-old man has weakness extending his right great toe and numbness over the dorsum of the right foot. Ankle dorsiflexion is 4/5. The straight leg raise is positive on the right. Patellar and Achilles reflexes are normal. Which nerve root is most likely affected?
A 55-year-old woman has progressive hand clumsiness and leg stiffness. Examination shows 4+ patellar reflexes bilaterally, sustained ankle clonus, positive Babinski bilaterally, and a positive Hoffmann sign on the right. Arm strength is mildly reduced with spastic tone. Which pattern is present?
A 32-year-old office worker has numbness in the thumb, index, and middle fingers and weakness of thumb opposition. Biceps strength and triceps reflex are normal. Phalen test reproduces her symptoms within 30 seconds. Which diagnosis is most likely?
A patient cannot dorsiflex the right ankle (grade 2/5) but can plantarflex normally. Pinprick is decreased over the medial malleolus and medial foot. The patellar reflex is diminished on the right compared to the left. Which nerve root is most likely involved?